The present invention relates to an optical communication link that uses an optical fiber for performing wavelength-division multiplexing (WDM) optical transmission.
To increase the transmission capacity of an optical fiber, there are extensively studied techniques of performing WDM optical transmission. In particular, recently, there has been also studied an ultrafast WDM optical transmission system whose channel transmission speed is 40 Gbps or faster.
In general, to realize a WDM optical transmission system, it is required that there occurs no unrecoverable waveform distortion at a relay point and in an optical reception apparatus. To attain this, it is conceived that the suppression of a nonlinear phenomenon in an optical transmission line and the reduction of accumulated dispersion are effective. Also, if there exist differences in dispersion value between wavelengths of respective optical signals, this leads to fluctuation of transmission quality caused by the difference of waveform distortion amounts among wavelengths. Accordingly, it is required to reduce changes in dispersion value (dispersion gradient) dependent on wavelengths in the optical transmission line as small as possible.
As a result, in many WDM optical transmission systems, there has been adopted an optical transmission line constructed by combining an optical fiber having positive dispersion (dispersion value) (hereinafter referred to as xe2x80x9cpositive dispersion optical fiberxe2x80x9d) with an optical fiber having negative dispersion (dispersion value) (hereinafter referred to as xe2x80x9cnegative dispersion optical fiberxe2x80x9d).
However, no conventional WDM optical transmission system, which is capable of suppressing a nonlinear phenomenon in an optical transmission line and sufficiently reducing accumulated dispersion, has been put into practical use.
Also, to suppress the accumulated dispersion, and the fluctuation of unrecoverable waveform distortion, which is caused by interaction with accumulated dispersion and a nonlinear phenomenon, between wavelengths, it is also required to sufficiently reduce a dispersion gradient in an optical fiber constituting an optical transmission line. However, no optical transmission line, which is constructed by combining a positive dispersion optical fiber and a negative dispersion optical fiber that satisfy such requirements, has been put into practical use.
For the reasons described above, it has been extremely difficult to construct an ultrafast WDM optical transmission system.
The present invention is an optical communication link, which comprises an optical transmission line that is constructed by combining a positive dispersion optical fiber having a positive dispersion value with a negative dispersion optical fiber having a negative dispersion value, in a wavelength region to be used:
wherein a dispersion value of the positive dispersion optical fiber is 5 ps/nm/km or more and 15 ps/nm/km or less; and
wherein DPS values of both the positive dispersion optical fiber and the negative dispersion optical fiber are 250 nm or more, the DPS values being obtained by dividing dispersion values of the respective fibers at a wavelength of 1550 nm by a dispersion gradient.
Other and further features and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.